Finned tube



' E. s. LEA

May 4, 194a.

FINNED 'ruaa le y 7. 1945' INVENTOR. Eda/471a J1 Zea I A'rmRNm's.

lfatented May 4, 1948 izu'r orrlcs f FINNED TUBE Edward S. Lea,

Morrisvilie, Pa., assignor to Doyle & Roth Company, Long Island City, N. Y., a

partnership Emma Doyle composed of Peter F. Roth and Application July 7, 1945, Serial No. 603,633

My present invention relates to finned tubes for heat exchangers and aims to provide certain improvements in such tubes. More particularly it relates to an air cooling or refrigerant tube wherein the fins are formed of a metallic wire, preferably of'copper, spirally and tightly wound on the tube and secured in place thereon in heat exchanging relation thereto, for example, by being soldered or brazed in place.

Heretofore it had been considered impossible to form fins of less than one-quarter inch in height on a tube from ribbon, wire or the like. Where fins of less than one-quarter inch in height were desired such fins were either rolled, out or otherwise integrally formed fromthe tube stock.

However, to roll or cut a fin in a tube requires that the tube be of. considerable thickness, which adds greatly to the cost of the finned tube.

Accordingly, a primary object of my present invention is to provide a heat exchanger tube having all the desirable characteristics of a rolled or cut finned tube, but which can be produced at considerably less cost. A further object is to provide such finned tube wherein the pitch of the spiral forming the fins or the number of fins per inch can be controlled throughout the length of a given tube, as desired. is to provide such a-finned predetermined location tube wherein, at a on the tube intermediate the ends thereof, the fins may be more closely spaced than at others, so that the more closely spaced fins may constitute a bearing portion for a supporting sheet.

The foregoing and other objects of my invention not specifically set forth I accomplish by forming said fin from wire of substantially tri-. angular or wedge-shape cross-section with the largest altitude extending radially of the tube and being of a dimension at least twice that of the base width of the wire and spirally winding and securing said resulting fin in heat exchanging relation to the outer surface of the tube. The invention will be better understood from the fol lowing description when considered in connection with the accompanyin drawings, wherein:

Figure 1 is a plan view of a finned tube embodying my invention.

Fig. 21s a sectional view of a fragment of the tube of Fig. 1 on an enlarged scale showing the fins uniformly spaced along the tube.

Fig. 3 is a view similar to Fig. 2 showing a portion of the tube with the fins more closely spaced than at other portions of the tube. r

Fig. 4 is a perspective view of a piece of wire from which the fin is formed.

A still further object 2 Claims. (Cl. 257-262) Fig. 5 is a heatexchanger having a bank of tubes showing the manner in which the bearing portion of the finned tube cooperates with a tubesupporting sheet.

The finned tube of my present invention may be used in any type of heat exchanger and primarily consists of a metal tube l0. preferably a seamless copper tube, upon the outer surface of which a helical fin II is spirally wound and secured in place in heat exchanging relation by being soldered or brazed thereto. Tubes of this general character have heretofore been made by winding a strip or ribbon oi. metaLusually onequarter inch or more in width, on edge around the tube with a lead of between one-quarter inch to one-tenth inch, and then applying solder to hold the fin in place. In forming such a finned tube, however, owing to the greater linear dimension of the fin at itsouter periphery as compared with its inner periphery, it was found thatthe outer eriphery would either curl in stretching, or conversely, the inner periphery would buckle, or both conditions would result, and means had to be employed to straighten the fin and hold it in position while it was being soldered in place.

the use of straightening means interfered with. the winding operation and rendered such fin formation impracticable. To overcome this condition and at the same time eliminate all need for employing fin straightening means, I form the fin from wire i2 (Fig. 4) having a substantially triangular or wedge-shape cross-section using the largest altitude dimension of the triangular wire as the height of the fin and the smallest dimension of the triangular wire as the base of the fin. Preferably the altitude dimension l3 of the triangle is at least twice and up to five times that of the base dimension ll so that, when the wire is spirally wound about the tube It the base It will provide a firm, non-buckling support for the fin while the apex, which is thin, will stretch quite readily without curling, to provide the increased linear dimension of the fiin at its outer periphery. Any suitable means may be employed for tightly winding the wire on the tube and holding it in place thereon while it is being secured by soldering or brazing onto the tube.

Although the tube is shown in Fig. 1 as havarea between the fin and a I ing plain ends, it will be obvious to those skilled in the art that the ends of the tube may be shaped or formed in various ways depending upon the type of connection the tube is'to make with its carrier or support; The fin, for certain portions of its length, to wit, within the bracketed portions a, is alsoshown as having its adjacent convolutions spaced apart at their base to expose prime portions of the tube in heat exchanging relation to the surrounding medium and at intermediate portions of its length, to wit, within the bracketed portions b as having its adjacent'convolutions much more closely spaced apart, and, in fact, at the inner periphery or base of the fin the adjacent convolutions of the fin maybe in abuttingrelation, for a purpose which will be presently explained.

By using wire of the character specified having an altitude dimension up to three-sixteenths inch and a base dimension between .025 and .035 of an inch, it will be appreciated that a wide range in the height of the fin and in the pitch or lead of the fin helix can be obtained. For example, by making the base width of the wire. .025 of an inch it is possible to provide a fin having twenty convolutions to the inch with the adjacent convolutions spaced apart at their base a distance equal to the base width of the fin. By spacing the adjacent convolutions of the base of the fin a greater or lesser distance, the number of convolutions per inch of tube can be decreased or increased, as desired. Thus, if a wire of the stated base .dimension is wound so that adjacent convolutions of the fin at the base thereof are in abutting relation, it will be possible to provide forty convolutions to the inch. Likewise, if the base width of the wire is .035 of an inch it would provide approximately twenty eight and one-half convolutions to the inch where the adjacent convolutions of the fin at the base are in abutting relation.

A finned tube having so large a number of convolutions per inch of tube offers a me'ans'for supporting finned tubes of substantial length within a shell and tube type heat exchanger as shown in Fig. 5, wherein a bank of finned heat transfer tubes III are shown as supported at their ends in a header plate mounted within a shell IS, the tubes being supported at portions intermediate their ends by a supporting plate H which is welded to angle'irons l8 which are connected to the header plate IS. The supporting plate or plates I! are formed with circular openings l9 which are equal to or slightly larger in diameter than the fins II and through which openings the finned tubes extend and are supported by the walls of the openings. heat exchangers of this general type it was found that the edges of the fins did not present enough area to give a firm bearing with the supporting sheet, and various means have been resorted to to overcome this deficiency. According to my present invention, however, by having the convolutions of the fins closely spaced apart so as to provide between twenty-eight and forty convolutions to the inch, I provide ample bearing the supporting sheet. Moreover, because of the triangular cross-section of the fins, the convolutions are very rigid and In prior constructions of from the tube due to the movement of the tubes relatively to the supporting sheet under conditions of expansion and contraction of the tubes.

It will accordingly be appreciated that I have provided a simple, efflcient and novel finned tube which possesses all of the advantages of a rolled, out or otherwise integrally formed fin, while at the same time affording the use of a thinner tube and possessing the added advantages of rendering it possible to readily vary the pitch or lead of the fin, ascircumstances and conditions dictate. In this connection,it may be stated that the fins may be readily wound on the tube on an ordinary lathe, the pitch or lead of the fin being controlled by varying the gear ratios. It is also feasible in thisway to wind a portion of the fin with the adjacent convolutions spaced apart at their base for a given portion of the tube length and with the base portions of adjacent convolutions'ln abutting relation for other and preferably intermediate portions of the tube length.

Although I have shown and described certain preferred embodiments of my invention it will be understood that changes in the specific details of construction, thereof may be resorted to without departing. from the spirit of the invention as defined in the appended claims.

What I claim is:

1. A tube for a heat exchanger comprising a metal tube having a helical fin spirally wound and bonded in place on the outer surface of the tube in heat exchanging relation thereto, said fin being formed of wire of substantially triangular or wedge-shaped cross-section, with the largest altitude dimension of the triangular wire extending substantially radially of the tube and with the smallest dimension of. the triangular wire constituting the base of the fin and extending substantially longitudinally of and being in contact with the tube, the altitude dimension being no greater than of an inch and being approximately between two and five times the base,

.length of the fin the convolutions at their base resist bending of the fin and loosening of the fin being in substantially abutting relation to provide a bearing portion for a supporting sheet.

2. A tube according to claim 1 wherein the 'adjacent convolutions of the fin for a major portion of the length of the fin are spaced apart at their bases axial distances approximately equal to the base width of the fin.

EDWARD S. LEA.

REFERENCES CITED The following references are of record in the file of this patent: 

